There is an image forming apparatus that forms a multicolor toner image. The image forming apparatus is arranged with multiple image forming units that form different color toner images on the peripheral portion of an intermediate transfer belt. For example, each image forming unit includes a photoconductive drum. A charger, a light exposure unit, a developing device, a cleaning unit, a static electricity discharger, and the like are arranged around the photoconductive drum.
In most cases, the image forming apparatus includes four color image forming units for yellow, magenta, cyan, and black colors. However, the image forming apparatus may include an image forming unit for fifth color other than yellow, magenta, cyan, and black. For example, the fifth color image forming unit may form a toner image with a gold toner or a silver toner, which may not be reproduced with the four color toners. For example, the fifth color image forming unit may form a toner image with an erasable toner that causes the image to be erasable.
A fifth color image may be an image in the fifth color only. A fifth color image may overlay a full color image formed with the four colors.
The image forming apparatus including five color image forming units has a different frequency of use for each image forming unit. For example, the black image forming unit forms a monochrome image in addition to a full color image. Thus, the frequency of use of the black image forming unit may be high. The frequency of use of the fifth color image forming unit, for example, may be low in comparison with the other four colors.
Inmost cases, the photoconductive drum of an image forming unit having a low frequency of use is brought into contact with the intermediate transfer belt without a toner therebetween. Thus, the photoconductive drum is likely to be degraded.
Separating the photoconductive drum from the intermediate transfer belt is also considered when images are not formed. However, a problem arises in that a complicated mechanism is required to separate each photoconductive drum from the intermediate transfer belt individually.